In the related art, indoor machines are usually divided into two parts through series connection to realize a constant-temperature dehumidification technology of an air conditioning system; during dehumidification, one part of the indoor machines act as a condenser, while the other part thereof act as an evaporator. However, when the air conditioning system is in normal operation, a refrigerant flow path will becomes very long, which affects the performance of the air conditioning system in normal operation and is not energy-saving and environmental friendly.